In data communications systems, it is often useful to modularize interface electronics and other interface elements in a data communication module. For example, in an optical data communication system, an optical data transceiver module may include a light source such as a laser, and a light detector such as a photodiode, and may also include driver and receiver circuitry associated with the laser and photodiode. The laser and associated circuitry convert electrical signals that the module receives via electrical contacts into optical signals that the module outputs via one or more optical fibers. The photodiode and associated circuitry convert optical signals received via the one or more optical fibers into electrical signals that the module outputs via the electrical contacts.
Generally, there are two types of semiconductor laser devices: edge-emitting lasers and Vertical Cavity Surface Emitting Lasers (VCSELs). An advantage of VCSELs is that they can be tested economically at wafer level rather than chip level. Another advantage of VCSELs is their well-defined spot size, which promotes high coupling efficiency to optical fibers without the need to provide beam shape correction, thus facilitating economical packaging. Edge-emitting lasers also have advantages, such as high output optical power. Edge-emitting lasers remain the most commonly used laser in long-distance high-speed optical data transceivers.
An optical data transceiver module may be of a bidirectional type that transmits a modulated optical transmit signal having a first wavelength via an optical fiber and receives a modulated optical receive signal having a second wavelength via the same optical fiber. Such a module generally includes a wavelength-selective filter (also referred to as a beam splitter) to separate the transmit signal and the receive signal.
Coarse wavelength division multiplexing (CWDM) is a technique by which a single optical fiber can simultaneously carry two or more communication channels, each characterized by a unique wavelength. A CWDM optical transceiver module commonly interfaces with at least one fiber that carries two or more outgoing or transmit channels and at least one other fiber that carries two or more incoming or receive channels. The CWDM optical transceiver modules that are currently commercially available generally have either four or eight channels. One type of optical multiplexer that has been suggested for use in a CWDM optical transceiver module includes four edge-emitting lasers, four corresponding narrowband optical filters, and three reflectors that redirect optical signals from one optical filter to another in a daisy-chain fashion. The four edge-emitting lasers must be precisely aligned so that their emitted signals that bounce among the reflectors and filters are ultimately coupled into the end of the fiber. The multiple bounces that some of the optical signals experience results in significant insertion loss. The difficulty in achieving sufficiently precise laser alignment and filter passbands can result in low manufacturing yield.
It would be desirable to provide a wavelength-multiplexed optical transceiver module that has low insertion loss and high manufacturing yield.